Deform mesh along another mesh without distortion
Simple Deform will give you slightly different results if the objects are not exactly the same. Not very good at deforming multiple objects and keeping them together as far as I know D:
Try this instead:

Select the first or last control point of the curve.
Scale the control point with ALT+S or through the N Panel.
Select ALL curve points and Right Click to bring up the Context Menu
Select Smooth Curve Radius.

Note that this aligns the curb way better, but it's still deformed. Everything you want is certainly possible, but doing it in a way that's 100% non-destructive and easy to modify and without deforming the curb width... all of that at the same time requires a not so simple setup or a more destructive approach unfortunately (or learning Houdini).

If you don't mind being more destructive, you can Shift+D to duplicate the edges of your road (you will have to apply your modifiers to create real geometry first). Then convert those edges to curves and use these new curves as paths for your curbs to follow.